Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, an inkjet printing apparatus and a data generating apparatus. In particular, the present invention relates to an image processing for reducing the density unevenness caused by the variation in the ejecting amounts among a plurality of nozzles for ejecting ink.
Description of the Related Art
Printing heads used in ink jet-type printing apparatuses may vary, due to errors during the manufacture thereof for example, among a plurality of nozzles with regard to the ejecting amount. Such a variation tends to cause the resultant printed image to have density unevenness.
Conventionally, as a processing for reducing such a density unevenness, the use of a head shading technique as disclosed in Japanese Patent Laid-Open No. H10-013674 (1998) has been known. This head shading corrects image data depending on the information regarding the ejecting amounts of the individual nozzles. By this correction, the number of ink dots that are finally printed can be increased or reduced to thereby adjust the density in the resultant printed image.
However, when the head shading technique as described above is used to reproduce a multi dimensional color by superposing two or more types of inks, a so-called color difference may be caused where a region printed by a nozzle having a varied ejection amount has a different color from an originally-intended color to be printed. For example, a case will be described where dots by cyan ink and magenta ink are printed to print a blue image. In a region where the variation of the ejection amount of nozzles causes the printing of magenta ink of a higher-than-standard ejection amount, magenta ink dots are larger than a standard size. At the same time, the correction by the head shading causes a lower-than-standard number of dots of magenta ink to be printed in this region. As a result, this region includes both of cyan dots and other dots consisting of blue areas and the surrounding magenta areas. Consequently, a color of this region differ from a color of a region including blue dots by cyan ink and magenta ink for which no variation of the ejection amount are cased (an originally-intended color to be printed).